Compressor provided with an improved piston

ABSTRACT

Electric compressor comprising a piston provided with a respective head and a valve plate mounted between the head and the body of the cylinder and provided with a gas suction port, the head being provided with a protrusion adapted to be intermittently introduced in the suction port substantially in the top dead-center position of the piston. The piston is provided externally, in the portion thereof which is opposite to the head side, with a recess that is accessible from the outside and is orientated towards the inner volume of the piston, the recess penetrating the body of the piston down to a depth which is at least equal to the height of the protrusion above the plane of the head.

DESCRIPTION

The present invention refers to a particular embodiment of analternating-motion piston reciprocating in a respective cylinder.

To more effectively exemplify and more clearly illustrate the invention,said piston is assumed to work in close association with a compressorfor refrigerators, in particular household-type appliances, without thishowever limiting the scope of the invention solely to such anapplication or connection.

It is a largely known fact that, in view of improving the thermodynamicefficiency of compressors, it is absolutely necessary for the volume ofthe discharge port, which is not affected by the displacement of thepiston, to be as small as possible. The reasons behind such arequirement are well known to those skilled in the art, so that theyshall not be dealt with any longer here.

In view of artificially reducing such a volume, the practice is known inthe art, for instance from the disclosure in U.S. Pat. No. 5,149,254, ofproviding, on the head of the related piston, a protrusion (post 54)that is so arranged and sized as to enable said protrusion to almostfully penetrate into the discharge port when the piston reaches its topdead center, without this of course giving rise to any interference withother parts nearby.

This expedient enables the volume of the discharge port that can beoccupied by the gas to be temporarily reduced in an artful manner, butto a quite considerable extent, so that the overall compressorefficiency can actually be boosted sensibly, as already mentioned above.

The above solution is certainly simple, reliable, economic and safe;however, in the course of the highly automated production of this kindof pistons a number of practical drawbacks tend to emerge, as describedbelow in greater detail.

The grinding operation on the outer cylinder of said compressor pistonsis carried out by means of a grinding technique without a fixed andsecured center of rotation; the same process is generally used forproducing millions of cylindrical parts such as the cylindrical rollersof roller bearings.

The grinding process essentially consists in a continuous sequence ofsaid pistons carried by conveying means through a plurality of grindingwheels or similar means being abraded by the action of said plurality ofgrinding wheels or similar means.

The size, orientation and number of said grinding means are such as toenable the pistons conveyed into such a processing step to be sent therein sequence with their axes coinciding with and parallel to thedirection of the motion thereof through said plurality of grindingmeans.

However, if the pistons happen to be arranged in contact with eachother, in the sense that the head of one such piston is in contact withthe rear edge of the neighbouring piston, then a serious drawback arisesin that, owing to the afore mentioned protrusion, said pistons tend toassume a position which is slightly inclined with respect to thedirection of motion. The result is that they would come up obliquely infront of or with respect to said grinding means and, therefore, wouldpractically prevent the grinding process from being carried out.

In view of eliminating such a drawback, said pistons are thereforespaced from each other so that the protrusion thereof is prevented fromtouching any other piston. Such a very simple and effective measure ofspacing the pistons from each other, however, has the effect of slowingdown and, therefore, decreasing the productivity of the grindingoperation, since the pistons must be cadenced into the process at a muchlower rate, owing to the need for their forward speed to be maintainedunaltered, while the "virtual" length thereof, ie. the length includingboth the actual length of the piston and the intermediate space thatseparates it from the subsequent piston in the sequence, is on thecontrary increased, as this is best illustrated in the accompanying FIG.1.

It therefore would be desirable, and is actually a main purpose of thepresent invention, to provide a technical solution that, when applied tosuch a compressor piston, does away with the above described drawback ina simple, low-cost and reliable manner. Such an aim shall furthermore bereached through the use of techniques and materials that are simple andreadily available on the market, while avoiding to affect theperformance capabilities and the overall reliability of the relatedcompressor to any extent.

According to the present invention such aims are reached in a piston ofthe kind described below by way of non-limiting example with referenceto the accompanying drawings, in which

FIG. 1 is a symbolic representation of a piston grinding plant accordingto state-of-art technology;

FIG. 2 is a symbolic representation of the same piston grinding plantaccording to the present invention;

FIG. 3 is a view from the opposite side of the head of a pistonaccording to the present invention;

FIG. 4 is a longitudinal-section view of the same piston shown in FIG.3;

FIG. 5 is a view from the head of the same piston;

FIG. 6 is a sectional view of two pistons according to the presentinvention, in which the head of one of them is in contact with thebottom portion of the other one.

With reference to FIG. 1 the grinding process can be noticed to becarried out presently by making use of at least two wheels, ie. anadjustment wheel 1 and an actual grinding wheel 2. Between said wheels,which rotate on parallel axes, a plurality of pistons 3 are caused topass in a sequence, preferably carried therethrough on a belt 4 or anyother equivalent conveying and support means.

In view of preventing the protrusion of each piston head frominterfering with the contiguous piston as mentioned above, each pistonis spaced from the next one by a separation interval 5 obtained throughproper cadencing and separating means 6 that are largely known in theart.

It can be readily appreciated that, if in this case the forward-movingrate of the pistons is 700 mm/min, the piston length is 23 mm and thedistance of each piston from the next one is 25 mm, then the pistonoutput cadence will amount to:

700/(23+25)×60=875 pistons/hour

However, if said pistons could be sent to such a grinding operationwithout any spacing being provided between them and, therefore, in closecontact with each other, as this is symbolically illustrated in FIG. 2,then, all other conditions remaining unaltered, said piston output ratewould amount to:

700/23×60=1826 pistons/hour ie. obtaining in this way an hourly outputthat is far more than the double value of the one achievable withprior-art technology.

According to the invention, the possibility of feeding the pistons togrinding with the head of each piston in close contact with the bottomof the contiguous piston, wherein each such piston head is provided withthe afore described protrusion, is obtained by providing each pistonwith a substantially cylindrical recess 7 provided on the side of thepiston which is opposed to the head 8 thereof, as this is bestillustrated in FIG. 4, so as to make it possible, by arranging thepistons against each other and oriented in the same direction, for theprotrusion on the head of a piston to freely enter, without anyconstraint and in any angular position of the same pistons, in saidrecess of the contiguous piston, thereby obtaining that saidprotuberances do not interfere with the contiguous pistons, whichtherefore can maintain the same axis and, at the same time, remain inclose contact with each other.

To such a purpose, said recess must have following features: it shallfirst of all extend inside the body of the piston for a depth that is atleast equal to the height of the protrusion 9 from the level of the head8; furthermore, said recess shall be capable of accomodating theprotrusion of the contiguous piston, such as this is illustrated in FIG.6, regardless of the position in which the pistons may find themselvesin relation with each other in the direction of rotation with respect tothe common axis 10. This practically not only enables the pistons to bedelivered to the grinding line regardless of the actual angular positionor orientation thereof, but also makes it possible for each piston fullyfree to rotate during grinding and transport, independently of the twopistons that precede and follow it.

Such a link-up can be obtained with a recess 7 that provides, toward theouter cylindrical surface of the piston, a circular edge 12 having nolarger thickness than the minimum distance between said protrusion 9projecting from the head of the piston and the circular edge 13 of thesame head.

Given such constraints, it can be readily appreciated that such a recesswill preferably have a cylindrical shape. However, such a recess mayalso be given any other appropriate shape, provided that it enables thebasic requirement placed on the same recess to be met, ie. thecapability thereof to fully accomodate said protrusion thereinto.

In such a case, said recess comes to be situated in front of a cavity 20provided within the body 21 of the piston and adapted to accomodate saidgudgeon pin 22 made integrally with the head 23 of the respectiveconnecting rod 24.

What is claimed is:
 1. Electric compressor, comprising a cylinder body,a piston provided with a respective head (8), a valve plate arrangedbetween said head and the body of said cylinder and provided with a gassuction port, said head being provided with an excentric protrusion (9)capable of being intermittently inserted in said port, said piston beingprovided, in the portion thereof which is opposed to the head side, witha recess (7) that is accessible from the outside and is oriented towardsthe inner volume of said piston, characterized in that said recessextends into the body of said piston down to a depth that is at leastequal to the height of said protrusion (9) above the plane of said head.2. Electric compressor according to claim 1, characterized in that saidrecess has a substantially cylindrical shape having its axis (10)coinciding with the axis of the piston, said recess being furtherdelimited externally by a circular edge (12) that constitutes theterminal portion of the cylindrical surface of the piston opposed tosaid head, the thickness of said circular edge being not greater thanthe minimum distance between said protrusion (9) projecting from thehead and the circular edge (13) of the same head.
 3. Electric compressoraccording to any of the preceding claims, characterized in that saidrecess (7) is made integrally with said piston.